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The Rishonim say that the "evil brother" is the tribe of Dan, who were guilty of the Idol of Michah.

The Midrash explains that אחירע is derived from באחו and רעוא, and means "Fertile Land."

The Ohr haChaim plays off the above two, and explains that the name means "my brother[s' land] is bad," from the fact that the tribe of Naphtali viewed their brothers' inheritance as less fertile and bad in comparison to their own allotment.